(Received 21 August 2013;accepted 22 August 2013;online 31 August 2013)

In the title di­hydro­dioxin, C31H28O5, the dioxane ring has a chair conformation, whereas each of the pyran and dioxine rings has an envelope conformation with methyl­ene and quaternary C atoms, respectively, being the flap atoms. The phenyl rings are cis and form a dihedral angle of 82.11 (10)°. The molecular structure is stabilized by C—H⋯O contacts. In the crystal packing, supra­molecular layers parallel to (101) are sustained by C—H⋯π inter­actions.

Isomeric, lapachol, 2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone, β-lapachone, 2,2-dimethyl-3,4-dihydro-2H-benzo[h]chromene-5,6-dione, and α-lapachone, 2,2-dimethyl-3,4-dihydro-2H-benzo[g]chromene-5,10-dione, Fig. 1, are found in the wood of trees of the genus, Tabebuia (family Bignoniaceae), distributed throughout Central and South America. Since their discovery at the end of the 19th century, lapachol and its isomers have attracted much attention due to their biological activities (de Almeida, 2009; Ferreira et al., 2010). Studies have revealed the effectiveness of these compounds and their derivatives as anti-cancer and anti-neoplastic (de Almeida, 2009), anti-fungal (Medeiros et al., 2010) and anti-Trypanosoma cruzi agents (Neves-Pinto et al., 2002), among other activities.

The quinone O atoms in lapachol and the lapachones are active sites and reactions at these sites have led to various derivatives, including oximes (da Silva et al., 2011), α-diazocarbonyls (Ferreira et al., 2006), phenazines (Neves-Pinto et al., 2002) and as we report here, a dihydrodioxin, (I), which was obtained by photoaddition of β-lapachone to 5,6-diphenyl-2,3-dihydro-1,4-dioxine, Fig. 2. Dihydrodioxins, most readily formed by a photochemical reaction between ortho-quinones and alkenes (Schönberg & Mustafa, 1944), are able to perform efficient DNA photo-cleavage (Mack et al., 2004). The crystal structure of β-lapachone has been reported (Cunha-Filho et al., 2006).

In (I), Fig. 3, the pyran ring approximates an envelope conformation with the C3 atom being the flap atom. The dioxine ring also has an envelope conformation where the C16 atom is the flap. With respect to this ring, the C17- and C23-bound phenyl rings are in axial and equatorial positions, respectively, and make a dihedral angle of 82.11 (10)° with each other. The orientation of these rings is such to facilitate the formation of intramolecular C—H···O interactions, Table 1. Finally, a chair conformation is found for the dioxane ring.

The major feature of the crystal packing is the formation of supramolecular layers parallel to (1 0 1) and sustained by C—H···π interactions, Table 1. These stack with no specific intermolecular interactions between them, Fig. 4.

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Acknowledgements

The use of the EPSRC X-ray crystallographic service at the University of Southampton, England, and the valuable assistance of the staff there is gratefully acknowledged. BB and JLW thank CAPES (Brazil) for support. Dr Maira Fasciotti, Inmetro (Brazil), is gratefuly acknowledged for the HRMS analysis. Support from the Ministry of Higher Education, Malaysia, High-Impact Research scheme (UM.C/HIR-MOHE/SC/12) is also gratefully acknowledged.

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